1. Field of the Invention
The present invention relates to a pressure sensor that has an internally disposed acceleration sensor.
2. Description of the Related Art
Pressure sensor devices have come into use in conjunction with recent technological developments. An example of a known conventional pressure sensor is disclosed in Japanese Laid-Open Patent Application No. 56-27630. FIG. 1 is a cross-sectional view showing a structure of a pressure-sensing element disclosed in Japanese Laid-Open Patent Application No. 56-27630. As shown in FIG. 1, this conventional pressure sensor is formed so that a spacer 101 is disposed between a peripheral part of a pair of facing diaphragms 100, and the diaphragms 100 face each other across a gap of suitable length. The diaphragms 100 are composed of glass, a ceramic material, a metal, or the like. When the diaphragms 100 are not electrically conductive, electrodes (not shown) are provided to the facing inner surfaces. When an external pressure is applied to the diaphragms 100 in such conventional pressure sensors, the diaphragms 100 bend, and the capacitance between the diaphragms 100 gradually increases. The applied pressure can be measured by determining this capacitance. In Japanese Laid-Open Patent Application No. 56-27630, temperature variation in the capacitance itself is suppressed by using a spacer 101 composed of materials having as low a linear expansion coefficient as possible; and temperature variation in the bending amount is suppressed by selecting a suitable material for the diaphragm. A pressure sensor that is minimally susceptible to temperature variation can thereby be obtained.
Additionally, a liquid crystal display device in which a capacitance value-detecting sensor is provided as a pressure-detecting sensor is disclosed in Japanese Laid-Open Patent Application No. 11-259234. In this liquid crystal display device, a display area is configured by placing a liquid crystal layer between a first substrate and a second substrate that are disposed facing each other. This area is provided with a pressure-detecting sensor for detecting pressure applied to pixels and outputting the detection data to the surface of the pixels on the liquid crystal layer side of the first substrate.
However, in the above-described prior art, a separate type of sensor is not incorporated into the pressure sensor. In other words, a pressure sensor and, e.g., an acceleration sensor are provided as separate devices. Examples of such devices include conventional TPMSs (tire pressure monitoring systems). In order to conserve energy in a TPMS, a tire pressure sensing circuit and a data transceiving circuit operate from the time the tires rotate. To measure the pressure, an acceleration sensor for detecting the rotation of the tires must be provided separately.